1. Field of the Invention
The present invention relates to an organic light emitting display and a method of fabricating the same, and more particularly, to an organic light emitting display having high resolution and high reliability and a method of fabricating the same.
2. Discussion of the Related Art
An image display, which displays various pieces of information on a screen, is key technology of the information age and is being developed toward lightweight, portable and high-performance trends. Thus, a flat display, which may reduce weight and volume, i.e., disadvantages of CRTs, has been spotlighted.
A flat display includes thin film transistors formed on a substrate and used as switching elements and driving elements. The thin film transistor includes an active layer forming a channel area, a gate electrode overlapping the channel area, and source and drain electrodes disposed opposite each other with the channel area interposed therebetween.
In such an active layer, an amorphous silicon thin film is deposited on the substrate and is crystallized into polycrystalline silicon by heat treatment. In more detail, if laser light is radiated onto the amorphous silicon layer, cooling is carried out via momentary dissolution and coagulation processes and thus, polycrystalline silicon cores in a solid state are generated. Further, a growth process in which a solid and liquid interface proceeds in the upward direction and transverse direction of the polycrystalline silicon cores according to a temperature gradient is carried out. In such a coagulation process, grains in the solid state grown in three or more directions meet on one line and such an interface forms a grain boundary. However, since the amorphous silicon layer dissolved by laser light has a high coagulation speed and a space to receive volume expansion according to changes between the solid and liquid states of the amorphous silicon layer is insufficient, the amorphous silicon layer at a point in which the grain boundaries formed by core growth in three or more directions meet, i.e., an active layer 16, protrudes upwards and forms protrusions, as exemplarily shown in FIG. 1. Therefore, an electric field is concentrated upon the protrusions of the active layer 16 and causes dielectric breakdown of a gate insulating film 14 and thus, an electrical short between a gate electrode 18 and the active layer 16 occurs. Further, conventionally, a storage area and a storage electrode of the active layer 16 overlap each other with the gate insulating layer 14 interposed therebetween and form a storage capacitor over a substrate 1. Here, since the storage area of the active layer 16 is formed on a buffer layer 12 through a doping process executed separately from the channel area of the active layer 16 but is located at an area different from the channel area, high resolution is not acquired. Moreover, if a flexible substrate is used to make a panel thinner, current of the transistors may be degraded due to impurities, such as mobile charges introduced from the flexible substrate.